This invention relates to the detection of suspended particulate matter in a liquid, and particularly to particles of magnetic material suspended in lubricating fluid.
In engines and other machinery, early warning of potential failure of bearings or other lubricated components can prevent the machine's ultimate failure through replacing or servicing the failing component. This becomes particularly significant when aircraft engines and the like are considered where an engine failure can have disastrous consequences.
When a lubricated engine component begins to deteriorate, small particles of the component are dislodged and carried away in lubricating fluid such as oil that flows around the component. As the component becomes more worn, and therefore becomes more likely to fail, the dislodged particles become larger and more numerous. The detection of such particles in the lubricating fluid provides an indication of the condition of the engine. By monitoring the size and number of such particles, imminent engine failure can be predicted and thereby avoided.
One well known method of detection relies upon the entrapment of particles by a magnetic device. The magnetic device is typically placed in the system that circulates the lubricating fluid, such that the fluid passes in close proximity to the magnetic device. Particles in the fluid are usually derived from metal components, and will therefore be magnetic particles (i.e., particles capable of being magnetized). Therefore, the particles will be attracted to, and trapped by, the magnetic device.
In some cases the magnetic device is physically examined on a periodic basis to determine the quantity and size of the trapped particles. In other cases, the magnetic device generates an electrical signal after a certain accumulation of particles has occurred. Still other methods of detection generate an electrical signal each time a particle is trapped. The electrical signal is typically generated through a measurement of the self inductance of a magnetic coil placed in close proximity to the magnetic device, where the self-inductance of the coil is a function of the quantity and size of magnetic particles deposited on the magnetic device.
Another device for detecting magnetic particles uses a coil wrapped around a tube through which the lubricating fluid is passed. The self inductance of the coil is closely monitored. When a magnetic particle passes through the tube, and therefore through the center of the coil, the self-inductance of the coil will increase slightly in proportion to the size of the particle.